Photoconductive complex with hydroxy-nitrobenzoic acids and triarylmethane dyes

ABSTRACT

Photoconductive materials for electrophotography have been formed by blending a molecular compound produced by a charge transfer reaction of poly-N-vinylcarbazole and tetrachloro-pbenzoquinone, with at least one compound selected from the group consisting of 2,hydroxy-3,5-dinitrobenzoic acid, 2-hydroxy-3nitrobenzoic acid and 2-hydroxy-5-nitrobenzoic acid, and with at least one triarylmethane dyestuff. These photoconductive materials for electrophotography are not only characterized by high sensitivity and excellent image quality, but they also can be easily cast into films and possess good transparency.

United States Patent [1 1 Matsumoto et al.

[ PHOTOCONDUCTIVE COMPLEX WITH HYDROXY-NITROBENZOIC ACIDS AND TRIARYLMETHANE DYES [75] Inventors: Shoichi Matsumoto; Kazuhiko Kurematsu, both of Yokohama, Japan [73] Assignee: Tokyo Shibaura Electric Co., Ltd.,

Kawasaki-shi, Japan [22] Filed: Dec. 14, 1971 [21] Appl. No.: 207,981

[30] Foreign Application Priority Data Dec. 16, 1970 Japan 45-11880 [52} US. Cl. 96/l.6, 96/15 [51] Int. Cl G03g 5/06 [58] Field of Search 96/1 R, 1 PC, 1.5, 1.6

[ 56] References Cited UNITED STATES PATENTS 3,037,861 6/1962 Hoegl et al. 96/l.5

[451 Mar. 18, 1975 3,159,483 12/1964 Behmenburg et a1 96/15 3,162,532 12/1964 Hoegl et al. 96/l.5 3,287,120 11/1966 Hoegl 96/l.5 3,421,891 1/1969 Inami et al 96/l.6

Primary E.ranziner Ro1and E. Martin, Jr.

Photoconductive materials for electrophotography have been formed by blending a molecular compound produced by a charge transfer reaction of poly-N- vinylcarbazole and tetrachloro-p-benzoquinone, with at least one compound selected from the group consisting of 2,hydroxy-3,S-dinitrobenzoic acid, 2- hydroxy-3-nitrobenzoic acid and 2-hydroxy-5- nitrobenzoic acid, and with at least one triarylmethane dyestuff. These photoconductive materials for electrophotography are not only characterized by high sensitivity and excellent image quality, but they also can be ABSTRACT easily cast into films and possess good transparency.

5 Claims, No Drawings PHOTOCONDUCTIVE COMPLEX WITH HYDROXY-NITROBENZOIC ACIDS AND TRIARYLMETI-IANE DYES BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a photoconductive material for electrophotography having high sensitivity, excellent image quality, and good transparency, and which has good film castability.

2. Description ofthe Prior Art Inorganic materials, such as selenium or zinc oxide, and organic materials, such as poly-N-vinyl carbazole systems or polyacetylnaphthylene systems, have been used as photoconductive materials by the prior art. The organic photoconductive materials in particular have been considered to be especially attractive industrially, since they can be easily cast into films, they possess high flexibility which renders them easily handleable, and they can be formed at relatively low costs. Nevertheless, the conventional organic materials 'used for this purpose have demonstrated several undesirable defects which have prevented the attainment of higher image quality, and higher photosensitivity. For instance, although poly-N-vinyl carbazole has good spectral sensitivity in the ultraviolet region, its degree of sensitivity is so low that it has insufficient electrophotographic sensitivity under incandescent light exposure. Attempts have been made to improve this sensitivity by blending a small amount of tetrachloro-p-benzoquinone as a sensitizer, with the poly-N-vinyl carbazole, in order to shift the spectral sensitivity to the visible regions and at the same time to intensify the photosensitivity. However, these attempts have not been entirely successful, since they have resulted in compositions possessing rather poor resolution, and which are characterized by nonuniformity of image, strong edge effects, and staining of the non-imaged parts. In another piecemeal attempt to eliminate these defects, several dye sensitizers were further blended with the poly-N- vinylcarbazole/tetrachloro-p-benzoquinone mixture, but such attempts have been met with only limited suc cess. Thus, it is difficult to satisfactorily use these organic photoconductive materials for electrophotography purposes.

A need exists, therefore, for an electrophotography photoconductive material which is not only characterized by high sensitivity and excellent image quality, but also can be easily cast into films of good transparency.

SUMMARY OF THE INVENTION Accordingly, it is one object of this invention to provide an organic photoconductive material for electrophotography which is not only characterized by high sensitivity and excellent image quality, but also by easy film castability for films and good transparency.

This and other objects have now herein been attained by providing a photoconductive material for electrophotography formed by blending a molecular compound produced by a charge transfer reaction of poly- N-vinyl carbazole and tetrachloro-p-benzoquinone, with at least one compound selected from the group consisting of 2-hydroxy-3,S-dinitrobenzoic acid, 2- hydroxy-3-nitrobenzoic acid and 2-hydroxy-5- nitrobenzoic acid, and with at least one triarylmethane dyestufl'.

which is highly suitable for electrophotography.

It has now been found that when this molecular compound is blended with a derivative of benzoic acid and a dyesensitizer, a photoconductive material character ized by excellent electrophotography properties is obtained.

DETAILED DESCRIPTION OF THE INVENTION The above-mentioned molecular compound, which is the main component of the photoconductive materials of this invention, can be obtained quite easily, as follows:

A solution of poly-N-vinyl carbazole and a solution of tetrachloro p-benzoquinone is prepared. Both solutions are heated slightly and the poly-N-vinyl carbazole solution is added to the tetrachloro-p-benzoquinone solution while stirring vigorously. Stirring is continued for several hours and the combined solutions are concentrated slowly and left for several hours at room temperature. A non-soluble solvent, such as methylalcohol, is then added slowly to the mixed solution, while stirring, until a deep blue violet-colored deposit is produced as a fine suspension in the solution. The separated, refined and dried'deposit will be the charge transfer reaction product of poly-'N-vinylcarbazole and tetrachloro-p-benzoquinone. The reaction may conveniently be carried out at temperatures of about 50C. and in such solvents as chloroform.

A benzoic acid derivative compound, such as 2-hydroxy-3,S-dinitrobenzoic acid, 2-hydroxy-3- nitrobenzoic acid or 2-hydroxy-5-nitrobenzoic acid, is then mixed and blended with the molecular charge transfer reaction product in a ratio of 05-10 parts by weight of the benzoic acid derivative per parts of charge transfer reaction product.

0.05-2 parts by weight of a triarylmethane dyestuff per 100 parts by weight of the charge transfer reaction product is then added to the blend.

Suitable triarylmethane dyestuffs which can be used for this purpose include crystal violet, Brilliant-green, Victoria blue, Methyl violet, Malachite green, Acid violet 68, etc.

The photoconductive material of this invention can be further blended with p-ter-phenyl, diphenyl, diphenylchloride, dibutylphthalate, dimethylglycolphthalate, triphenylphosphate, methylnaphthalene or dioctylphthalate, etc. as a plasticizer to improve its filmforming capability.

The charge transfer reaction product, however, is a high molecular weight compound, which possesses good film formability and good flexibility even without the optional plasticizer, and it possesses good transparency and high sensitivity throughout the visible region. It is highly photoconductive itself, without any other additive, but when it is blended with one of the abovementioned benzoic acid derivatives, and at least one triarylmethane dyestuff, it becomes even more highly sensitive. Surprisingly, when this product is blended with only the benzoic acid derivative or with only the triarylmethane dyestuff separately, the degree of sensitivity and image quality tends to be lower, rather than improved.

The photoconductive film produced by the photoconductive material of this invention can be formed with good homogeneity and is characterized by good image reproducibility when exposed through any colored original incandescent light or other visible rays, and can form an image of good resolution and high uniformity. Moreover, when thesubstratum is moderately transparent, the image formed can be used as a socalled secondary master, as a substitute for a negative or a semitransparent master, Le, a diazo master or a copy master.

The reason why the photoconductive material of this invention has such'good photographic characterisitcs is not'fully understood, but seems to be explainable as follows: The charge transfer reaction product is formed from poly-N-vinylcarbazole and the tetrachloro-pbenzoquinone, which effectively overlap each other in molecular orbital electronic states. This is believed to have some effect in increasing the sensitivity. When this product is combined with the benzoic acid derivative and the triarylmethane dyestuff, the sensitivity becomes even greater. Moreover, the charge transfer reaction product which forms the matrix of the system is a high molecular weight material which possesses good miscibility in the blend and permits'the formation of a smooth and homogeneous photoconductive film.

Having now generally described the invention, a further understanding can be attained by reference to certain specific Examples which are provided herein for purposes of illustration only and are not intended to be limiting unless otherwise so specified.-

EXAMPLE A chloroform solution of poly-N-vinylcarbazole (hereinafter referred to as solution A) was prepared by dissolving 4.0 g. of poly-N-vinylcarbazole in 1.4 l. of

chloroform.

Another benzoquinone solution (hereinafter referred to as solution B) was prepared by dissolving 4,9 g. of tetrachlorop-benzoquinone in 1.0 l. of chloroform. Solution A was heated to a temperature of 50C. and was added dropwise into solution B which was also heated to a temperature of 50C. The mixing was accompanied by vigorous stirring. After the mixing of solutions A and B, stirring was continued for 3 hours and the temperature was maintained at 50C. The mixed solution was then concentrated slowly to a volume of 1 liter, and was left for 24 hours at room temperature.

160 ml. of methyl alcohol was then dripped into the concentrated solution, while stirring, and a deep blue Component acid Z-hydroxy-S-nitrobenzoic acid Crystal viol O.

Brilliant green Victoria blue Optimum exposure (lux.sec.)

chloroform solution of tetrachloro-p violet-colored deposit was produced as a fine. suspension in the solution. This deposit was separated from the solution, refined and dried. This was identified as a molecular compound produced by acharge. transfer reaction of poly-N-vinylcarbazoleand tetrachloro-pbenzoquinone.

0.5 g. of photoconductive material for electrophotography was prepared and dissolved in 9 ml. of achloroform-acetone mixed solvent (5 l). The solution obtained was added dropwise onto the surface of an aluminum plate (1 mm. in thickness), dried and formed into a photoconductive film (lOu in thickness); Six

photosensitive plates for electrophotography were prepared, and these plates'were given a positive electric charge by ordinary corona-discharge methods from a 5' kV. source. The plates were then exposed with incandescent light through an original, master by means of photographic enlarger, and were developed by cascading the toner. The optimum exposure of the photosen sitive plates for. electrophotography obtained as above described, was measured and is shown inTablel.

The optimum exposure described here, means the so-called optimum exposure required to obtain a faithful duplication ofthe original master of good resolution or good contrast, uniform image, stainlessness of the non-imaged portions and to produce acopy ofgood image quality without edge effects.

As controls for photosensitive plates prepared by blending of (l) PVCACHLO molecular compound, and (2) at least one compound selected from the group consisting of 2-hydroxy-3,S-dinitrobenzoic acid, 2- hydroxy-3-nitrobenzoic acid and 2-hydroxy-5- nitrobenzoic acid, was observed and measured experimentally and was measured for optimum exposure. The optimum exposure of materials prepared by blending (l) PVCACHLO molecular compound, and (3) a triarylmethane dyestuff, was observed and measured experimentally. The optimum exposures were both 90-160 luxisec. which was inferior or only as good as the optimum exposure of photosensitive plates pre- TABLE I SAMPLE 3 4 pared by (l) PVCACHLO molecular compound alone, which was about 100 lux.sec.

As another control, the optimum exposure of photosensitive plates prepared by blending poly-N- vinylcarbazole, and tetrachloro-p-benzoquinone, instead of l PVCA.CHLO molecular compound which was a main component of photoconductive material for electrophotography in each sample, was observed and measured experimentally, and found to be 700l,OOO lux.sec., respectively. The duplicated copy prepared was not only inferior in resolution and contrast, but had poor image uniformity and was highly stained in the non-imaged portion. Moreover, it was inferior in edge effect and image quality.

6 raphy comprising a blend of a. a molecular charge transfer reaction product of poly-N-vinylcarbazole and tetrachloro-pbenzoquinone,

b. at least one benzoic acid derivative selected from the group consisting of 2-hydroxy-3,5- dinitrobenzoic acid, 2-hydroxy-3-nitrobenzoic acid and 2-hydroxy-5-nitrobenzoic acid, and

c. at least one triaryl methane dyestuff.

2. The photoconductive material of claim 1, wherein the ratio of the benzoic acid derivative to said charge transfer reaction product is 0.5 to 10 parts/100.

3 The photoconductive material of claim 1, wherein the triayl methane dyestuff is selected from the group The photoconductive material of this invention is consisting of Crystal violet, Brilliant-green. Victoria blue, Methyl-violet, Malachite-green and Acid-violet 6B.

4. The photocondutive material ofclaim l which further contains a plasticizer selected from the group ,consisting of p-ter-phenyl, diphenyl, diphenylchloride, dibutylphthalate, dimethylglycolphthalate, triphenylphosphate, methylnaphthalene and dioctylphthalate.

5. The photoconductive material of claim 1 which contains 0.05-2 parts by weight of a triarylmethane dyestuff per parts by weight of said charge transfer reaction product.

=l l I 

1. A PHOTOCONDUCTIVE MATERIAL FOR ELECTROPHOTOGRAPHY COMPRISING A BLEND OF A. A MOLECULAR CHARGE TRANSFER REACTION PRODUCT OF POLY-NVINYLCARBAZOLE AND TETRACHLORO-P-BENZOQUINONE, B. AT LEAST ONE BENZOIC ACID DERIVATIVE SELECTED FROM THE GROUP CONSISTING OF 2-HYDROXY-3,5-DINITROBENZOIC ACID, 2-HYDROXY-3-NITROBENZOIC ACID AND 2-HYDROXY-5NITROBENZOIC ACID, AND C. AT LEAST ONE TRIARYL METHANE DYESTUFF.
 2. The photoconductive material of claim 1, wherein the ratio of the benzoic acid derivative to said charge transfer reaction product is 0.5 to 10 parts/100.
 3. The photoconductive material of claim 1, wherein the triayl methane dyestuff is selected from the group consisting of Crystal violet, Brilliant-green, Victoria blue, Methyl-violet, Malachite-green and Acid-violet 6B.
 4. The photocondutive material of claim 1 which further contains a plasticizer selected from the groUp consisting of p-ter-phenyl, diphenyl, diphenylchloride, dibutylphthalate, dimethylglycolphthalate, triphenylphosphate, methylnaphthalene and dioctylphthalate.
 5. The photoconductive material of claim 1 which contains 0.05-2 parts by weight of a triarylmethane dyestuff per 100 parts by weight of said charge transfer reaction product. 